Seems like I’m always getting calls from folks asking “How can I crack a geode open without breaking it into small pieces?” Well, there are a number of ways, some good and some not so good. Here, I will outline four of the most common ways. [By the way, it’s a good idea to use safety goggles whenever you start banging away at a rock.]
1) Diamond Saw – Should you be fortunate enough to have a large diamond saw, or know someone that owns one, you can saw the geodes in two. This works best when there is a vice to hold the specimen. You can cut the geode open and end up with two halves with a smooth face on each. (But not everyone has a diamond saw….)
2) Another method of opening geodes that works well, (the method I use most often) is to crack the geode open with an old fashioned cast-iron plumbing pipe cutter. This is a tool that plumbers used to use in doing plumbing in homes when they worked with the cast iron plumbing pipes. (Homes built prior to about 35 years ago.) I have one of these tools that I use to break geodes open and most of the time I can break them with two matching halves. This really does a good job.
Maybe you have seen show dealers that were breaking geodes open with one of these tools. The tool has a chain at the business end with links like a bicycle chain, and in this chain there are round carbide rollers with sharp edges on them.
To break the geode open, you simply wrap the chain, with the carbide rollers, around the geode, and fasten it into a notch in the tool and press down on the handle. This constricts the chain around the geode evenly all the way around and squeezes to where it breaks the geode open into two halves. I got my cast iron plumbing pipe cutter from a retired plumber here locally. If you’re going to break a lot of geodes you may want to get one.
3) Hammer and chisel. Most folks don’t have a diamond saw or plumbing pipe cutter, and only want to break a couple of geodes open. Well, you can do a pretty good job with a hammer and cold chisel. I’ve done it a number of times and it works well. Take your hammer, cold chisel and geodes outside where there is a concrete walk, driveway, steps, etc., in other words a hard surface. I wouldn’t try it on a wooden surface. And you almost need three hands to do this. Place the geode on the concrete and hold it on the sides with one hand, then hold the cold chisel on the top of the geode and strike it LIGHTLY with your hammer. Don’t try to break it open now…. Rotate the geode about a half inch, place the chisel in line with where you just hit it and strike the chisel again … LIGHTLY. Do this all the way around the largest part of the geode. By the time you have hit the chisel in a line all the way around the geode, it should be ready to open. If the geode has not broken open at this point, start around the circumference again, striking the geode with the cold chisel in a straight line. Strike the chisel a little harder this time. This is a little slow, but if you do it right and don’t get in too big a hurry, you should be able to break the geode open into two halves that you can fit back together to where you can’t tell where it was broken.
4) Hammer – Of course you can strike the geode repeatedly with the hammer until it breaks open, but, it most likely will end up in a few pieces. Not a good method!